TMPFS(5) FreeBSD File Formats Manual TMPFS(5)
NAME
tmpfs - in-memory file system
SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
options TMPFS
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
tmpfs_load="YES"
DESCRIPTION
The tmpfs driver implements an in-memory, or tmpfs file system. The
filesystem stores both file metadata and data in main memory. This
allows very fast and low latency accesses to the data. The data is
volatile. An umount or system reboot invalidates it. These properties
make the filesystem's mounts suitable for fast scratch storage, like
/tmp.
If the system becomes low on memory and swap is configured (see
swapon(8)), the system can transfer file data to swap space, freeing
memory for other needs. Metadata, including the directory content, is
never swapped out by the current implementation. Keep this in mind when
planning the mount limits, especially when expecting to place many small
files on a tmpfs mount.
When mmap(2) is used on a file from a tmpfs mount, the swap VM object
managing the file pages is used to implement mapping and avoid double-
copying of the file data. This quirk causes process inspection tools,
like procstat(1), to report anonymous memory mappings instead of file
mappings.
OPTIONS
The following options are available when mounting tmpfs file systems:
easize Set the maximum memory size used by extended attributes in
bytes. The default is 16 megabytes.
export Accept the export option for compatibility with nfsv4(4).
This option does nothing.
gid Set the group ID of the root inode of the file system. The
default is the mount point's GID.
inodes Set the maximum number of nodes available to the file
system. If not specified, the file system chooses a
reasonable maximum based on the file system size, which can
be limited with the size option.
maxfilesize Set the maximum file size in bytes. The default is the
maximum possible value.
mode Set the mode (in octal notation) of the root inode of the
file system. The default is the mount point's mode.
nomtime Disable the tracking of mtime updates caused by writes to
the shared mapped areas backed by tmpfs files. This option
removes periodic scans, which downgrade read-write-mapped
pages to read-only to note the writes.
nonc Do not use namecache to resolve names to files for the
created mount. This saves memory, but currently might
impair scalability for highly used mounts on large machines.
nosymfollow Do not follow symlink(7)'s on the mounted file system.
pgread Enable pgcache read for the mount.
size Set the total file system size in bytes, unless suffixed
with one of k, m, g, t, or p, which denote byte, kilobyte,
megabyte, gigabyte, terabyte and petabyte respectively. If
zero (the default) or a value larger than SIZE_MAX -
PAGE_SIZE is given, the available amount of memory
(including main memory and swap space) will be used.
uid Set the user ID of the root inode of the file system. The
default is the mount point's UID.
union Refer to mount(8).
EXAMPLES
Mount a tmpfs memory file system:
mount -t tmpfs tmpfs /tmp
Configure a tmpfs mount via fstab(5):
tmpfs /tmp tmpfs rw 0 0
SEE ALSO
procstat(1), mmap(2), nmount(2), unmount(2), fstab(5), mdmfs(8),
mount(8), swapinfo(8), swapon(8)
HISTORY
The tmpfs driver first appeared in FreeBSD 7.0.
AUTHORS
The tmpfs kernel implementation was written by Julio M. Merino Vidal
<
[email protected]> as a Google Summer of Code project.
Rohit Jalan and others ported it from NetBSD to FreeBSD.
This manual page was written by Xin LI <
[email protected]>.
FreeBSD 14.1-RELEASE-p8 September 18, 2023 FreeBSD 14.1-RELEASE-p8